html,
body,
div,
span,
applet,
object,
iframe,
h1,
h2,
h3,
h4,
h5,
h6,
p,
blockquote,
pre,
a,
abbr,
acronym,
address,
big,
cite,
code,
del,
dfn,
em,
font,
img,
ins,
kbd,
q,
s,
samp,
small,
strike,
strong,
sub,
sup,
tt,
var,
b,
u,
i,
center,
dl,
dt,
dd,
ol,
ul,
li,
fieldset,
form,
label,
legend {
    margin: 0;
    padding: 0;
    font-size: 100%;
    border: 0;
    outline: 0;
    background: transparent;
}

ol,
ul {
    list-style: none;
}

:focus {
    outline: 0;
}

#content {
    padding-top: 40px;
}

#content ul {
    width: 1200px;
    margin: 0 auto;
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
}

.btnbox {
    width: 1200px;
    margin: 0 auto;
    text-align: center;
}

#content ul li {
    margin: 20px;
    width: 200px;
    height: 180px;
}

#content ul li:last-child {
    margin-right: 0;
}

#content ul li a {
    position: relative;
    display: block;
    width: 100%;
    height: 100%;
    perspective: 800px;
}

#content ul li a > div {
    position: absolute;
    left: 0;
    width: 100%;
    height: 100%;
    color: #fff;
    overflow: hidden;

    transform-style: preserve-3d;

    transition: 0.8s ease-in-out;
    backface-visibility: hidden;
}

#content ul li a div:first-child {
    display: flex;
    justify-content: center;
    transform: rotateY(0);
    z-index: 2;
    border: 1px solid #2e7eee;
}

#content ul li a div:last-child {
    background: rgb(0, 188, 212);
    transform: rotateY(180deg);
    z-index: 1;
}

#content ul li a div h1 {
    text-align: center;
    line-height: 180px;
    font-size: 26px;
}

#content ul li a div img {
    max-width: 100%;
}

.rotatey180 {
    transform: rotateY(-180deg) !important;
}

.rotateyzero {
    transform: rotateY(0) !important;
}

.btn,
.btn-all {
    margin-top: 60px;
    display: inline-block;
    background: #2e7eee;
    border-radius: 10px;
    text-decoration: none;
    text-transform: uppercase;
    border: none;
    color: white;
    padding: 8px 16px;
    text-align: center;
    font-size: 16px;
    transition-duration: 0.4s;
    cursor: pointer;
}

.cardnum {
    position: absolute;
    font-size: 20px;
    left: 10px;
    top: 10px;
}

#gameText {
    text-align: center;
}
